Lasers and other light sources typically require optical elements to modify their optical output to suit a given application. From the earliest days in astronomy in the 1600s, scientists and engineers used round lenses inside a cylindrical tube to precisely mount the lenses on-center in x, y, and z axes, i.e., according to a Cartesian coordinate system or the like. This conventional approach is simple, accurate, and robust and readily transferable to laser systems.
It is common for optics used with lasers to be mounted in precision-machined tubes where the bores may have multiple internal diameters with sharp steps between each internal diameter change to manage the spacing of lenses. These step changes in internal diameter often serve two purposes: 1) to align a given lens radially so that its center matches the center of the optical source as well as other optical elements in the tube and 2) to position the linear distance of the lens precisely in relation to the optical source and other optical elements by having the laser mechanically built-up against the step within the tube. This approach serves the industry well, especially where the optical source divergence is radially symmetric and all corresponding optical elements can similarly be radially symmetric. In U.S. Pat. No. 4,060,309 the contents of which are incorporated herein in their entirety, Noane demonstrates the lens and tube method for alignment of laser optical elements. Prior to this, Eddy implemented this idea in U.S. Pat. No. 2,380,829, the contents of which are incorporated herein in their entirety.
Laser diodes, in particular, semiconductor laser diodes, typically have optical outputs that are not radially symmetric. These laser diodes typically have one divergence angle in the x-axis and a different divergence angle in the y-axis, where the z-axis denotes the path of optical travel. The x-axis is typically denoted with the lower angle of divergence and is often referred to as the “slow axis”. The y-axis divergence is typically assigned the higher divergence angle and is often referred to as the “fast axis”. Optical assemblies for laser diode systems are often designed to make use of a cylindrical tube for the alignment of lenses; however, care must be taken to mount the laser diode so that its optical emissions are centered within the tube and the optical lenses must be aligned radially to match the positions of the laser diode's fast and slow axes. The laser diode is typically mounted on a TO-can optoelectronics mount apparatus, referred to as “TO-can,” or the like, which has a flat surface to mount the laser diode chip and an outer round section to mount within the tubular optical alignment setup. This TO-can arrangement is designed such that the laser diode optical output is centered relative to the outer circular dimension of the TO-can which in-turn mates precisely with the tubular assembly. Typically, a separate lens assembly or the like is used for each of the fast axis and slow axis. However, some applications only lens one of the axes for their application. A single complex toric lens may be used to adjust the fast axis and slow axis using a single lens.
A laser diode assembly is demonstrated by Bean in U.S. Pat. No. 8,811,439, the contents of which are incorporated herein in their entirety, where the outside dimension of the TO-can is mounted within the cylindrical bore of a tube and precisely aligned to a lens also attached to the tube. The TO-can and lens are each inserted into opposite ends of the tube and rest against steps in the tube at each end which precisely determines the z-axis distance between these elements. Bean's laser diode assembly does not exactly describe how the radial alignment is done between the laser diode (mounted on TO-can) and the lens. In particular, no mention is made of radial positioning the TO-can within the tube. Therefore, radial alignment in this setup is still uncertain and may require an active alignment of these elements or precision fixtures during assembly to ensure angular alignment. Such active alignment or precision fixtures and assembly methods add significant cost and complexity to the system and may be prone to misalignment and subsequent performance drawbacks.